Comparative Study of Conventional Planning and MRI Based Volume Optimized Planning of Intracavitary Brachytherapy of Cervical Cancer

Author(s): Niharika Darasani1

BACKGROUND Cervical cancer is one of the commonest malignancies among women in India. The main stay of treatment is the combination of External Beam Radiation Therapy (EBRT) and Intracavitary Brachytherapy (ICBT) in these patients. We compared conventional point A based treatment planning and MRI based volume optimized planning in ICBT of cervical carcinoma along with doses to organs at risk in both plans. We also compared the radiation doses to organs at risk in both the plans by International Committee on Radiation Units (ICRU) recommended points and dose volume histograms. METHODS Eighteen Patients with cancer cervix (72.22% with stage IIB) received EBRT on linear accelerator by four field technique using 15 MV energy for a dose of 46 Gray (Gy) – 50 Gy in 23-25 fractions 2.0 Gy per fraction, five days per week, for 5 weeks to whole pelvis. Most of the patients received at least three doses of chemotherapy. A total of 50 high-dose rate intracavitary brachytherapy (HDR-ICBT) applications done in 18 patients were used for analysis in the study. Clinical history, gynaecology examination and punch biopsy were undertaken. The patients were assessed during EBRT after 2 weeks, for ICBT application and suitable patients were selected for the procedure. CT based point A planning and MRI based volume optimised planning were done for each ICBT application before intracavity brachytherapy. Contouring of rectum, bladder, right and left femoral heads, and small bowel were done. RESULTS The median age of patients in this study was 50.4 ± 03.25 years. 72.22% (13/18) of the patients were of stage IIB. The mean dose delivered to 90% high-risk clinical target volume (D90- HR-CTV) for all 50 applications by volume optimized planning was 06.87 ± 0.942 Gy. The mean D90-HR-CTV by point A based conventional planning was 13.69 ± 1.06 GY. The mean D100-HR-CTV by volume optimized planning was 05.30 Gy (± 0.20). The mean D100-HR-CTV by point A based conventional planning was 08.91 ± 0.74 Gy. Maximum doses in the bladder and rectum were significantly lower (p<0.05) for MRI planning than for the conventional approach (06.49 GY Vs. 07.45 GY) for bladder; (04.57 GY vs. 05.06 GY) for rectum respectively. Both bladder (D2cc) and rectum (D2cc) doses could be reduced significantly by volume optimization. CONCLUSIONS D90-HR-CTV adequately covered by MRI based volume optimized planning was superior to conventional point A based planning in terms of both conformity of target coverage and evaluation of Organ at Risk (OARs), including the rectum and bladder. Both bladder and rectum doses in the most irradiated 2cc volume are significantly reduced in volume optimized planning. Hence, volume optimized planning would be more beneficial in large volume diseases to get better target coverage at the same time sparing the organs in small volume diseases. Hence, the use of MRI-based volume optimization brachytherapy for patients with large volume tumours with parametrial invasion is beneficial.